http client
go封装了http客户端，请求远程数据非常方便，看些源码底层如何实现。
resp, err := http.Get("https://baidu.com") if err != nil { fmt.Printf("发起请求失败：%v", err) return }defer resp.Body.Close() io.Copy(os.Stdout, resp.Body)请求的大致流程
1.根据请求条件，构建request对象
2.所有的client请求，都会经过client.do()处理
func (c *Client) do(req *Request) (retres *Response, reterr error)
2.1 request请求使用client.send()处理
func (c *Client) send(req *Request, deadline time.Time) (resp *Response, didTimeout func() bool, err error)resp, didTimeout, err = send(req, c.transport(), deadline)//默认传DefaultTransport
3.send函数
func send(ireq *Request, rt RoundTripper, deadline time.Time) (resp *Response, didTimeout func() bool, err error) { resp, err = rt.RoundTrip(req) }4.DefaultTransport的RoundTrip方法，实际就是Transport的RoundTrip方法
func (t *Transport) roundTrip(req *Request) (*Response, error) { treq := &transportRequest{Request: req, trace: trace} //封装新的request cm, err := t.connectMethodForRequest(treq) pconn, err := t.getConn(treq, cm) //使用连接池技术，获取连接对象*persistConn， resp, err = pconn.roundTrip(treq) //使用连接对象获取response}5.使用连接池技术，获取连接对象*persistConn
func (t *Transport) getConn(treq *transportRequest, cm connectMethod) (pc *persistConn, err error) { w := &wantConn{ //构建连接对象 cm: cm, key: cm.key(), ctx: ctx, ready: make(chan struct{}, 1), beforeDial: testHookPrePendingDial, afterDial: testHookPostPendingDial, } if delivered := t.queueForIdleConn(w); delivered {//从连接池获取符合的连接对象，有就返回 pc := w.pc return pc, nil } t.queueForDial(w)//发起连接 select { case <-w.ready: //连接准备好，就返回连接对象 return w.pc, w.err}5.1 Transport.queueForDial发起连接
func (t *Transport) queueForDial(w *wantConn) { go t.dialConnFor(w)}5.2 发起拨号dialConnFor
func (t *Transport) dialConnFor(w *wantConn) { pc, err := t.dialConn(w.ctx, w.cm) //发起拨号，返回连接对象 delivered := w.tryDeliver(pc, err)}5.3 发起拨号
func (t *Transport) dialConn(ctx context.Context, cm connectMethod) (pconn *persistConn, err error) { pconn = &persistConn{ //构建连接对象 t: t, cacheKey: cm.key(), reqch: make(chan requestAndChan, 1), writech: make(chan writeRequest, 1), closech: make(chan struct{}), writeErrCh: make(chan error, 1), writeLoopDone: make(chan struct{}), } conn, err := t.dial(ctx, "tcp", cm.addr()) //tcp连接，获取到net.conn对象 pconn.br = bufio.NewReaderSize(pconn, t.readBufferSize())//可以从conn读 pconn.bw = bufio.NewWriterSize(persistConnWriter{pconn}, t.writeBufferSize())//写到conn go pconn.readLoop()//开启读协程 go pconn.writeLoop()//开启写协程 return pconn, nil}5.4读协程,虽然是for循环，但是一次性就把请求的response读完了，如果没有关闭，就会造成协程泄露了
func (pc *persistConn) readLoop() { alive := true for alive { rc := <-pc.reqch //读取request,写入的地方在步骤6 resp, err = pc.readResponse(rc, trace) //返回response //response的body是否可写，服务器code101才可写，所以正常这个是false bodyWritable := resp.bodyIsWritable() //response.Close设置循环结束，退出协程 if resp.Close || rc.req.Close || resp.StatusCode <= 199 || bodyWritable { alive = false } //把response写入通道，在步骤6会读取这个通道 select { case rc.ch <- responseAndError{res: resp}: case <-rc.callerGone: return } //循环结束的一些情况 select { case bodyEOF := <-waitForBodyRead: //读完body也会自动结束 case <-rc.req.Cancel: case <-rc.req.Context().Done(): case <-pc.closech: alive = false pc.t.CancelRequest(rc.req) } }5.4.1 pc.readResponse 获取response
func (pc *persistConn) readResponse(rc requestAndChan, trace *httptrace.ClientTrace) (resp *Response, err error) { for{ resp, err = ReadResponse(pc.br, rc.req) //获取response }}5.4.2 ReadResponse读取response
func ReadResponse(r *bufio.Reader, req *Request) (*Response, error) { tp := textproto.NewReader(r) //可以处理HTTP, NNTP, SMTP协议的内容，方便读取 resp := &Response{ Request: req, } line, err := tp.ReadLine()//读取第一行，获取协议，状态码 resp.Proto = line[:i] resp.Status = strings.TrimLeft(line[i+1:], " ") mimeHeader, err := tp.ReadMIMEHeader()//读取header头 resp.Header = Header(mimeHeader)}5.5 写协程
func (pc *persistConn) writeLoop() { for { select { case wr := <-pc.writech: startBytesWritten := pc.nwrite err := wr.req.Request.write(pc.bw, pc.isProxy, wr.req.extra, pc.waitForContinue(wr.continueCh)) }}6.使用连接对象*persistConn获取response
func (pc *persistConn) roundTrip(req *transportRequest) (resp *Response, err error) { var continueCh chan struct{} resc := make(chan responseAndError) //response通道 pc.writech <- writeRequest{req, writeErrCh, continueCh}//written by roundTrip; read by writeLoop pc.reqch <- requestAndChan{ //written by roundTrip; read by readLoop req: req.Request, ch: resc, addedGzip: requestedGzip, continueCh: continueCh, callerGone: gone, } for { //监听这些通道 testHookWaitResLoop() select { case err := <-writeErrCh: case <-pc.closech: case re := <-resc: //监听 response通道，返回response return re.res, nil } }}以上就是解析Go的http client的知识。速戳>>知识兔学习精品课！